Transponders and scanner systems are well known in the art. These systems generally include a scanner, or interrogator, which transmits signals to, and receives signals from, one or more transponders. The transponders may be active, in that they contain a power source such as a battery, or passive in that they receive power from an external source, such as through inductive coupling as can be the case with radio frequency technology. Passive transponders are commonly implanted in animals due to the fact that they do not rely on a self-contained power source. Such implantable, passive transponders often contain identification information for the animal. It is also known to have an implantable transponder coupled with a sensor, such as a temperature measurement device, such that the transponder is able to transmit both identification information, as well as information on the body characteristic of the animal.
The temperature measurement devices used in conjunction with these transponders have traditionally been thermistors. The resistance of the thermistor changes as a function of the temperature of the thermistor. Thus, using a properly calibrated thermistor, the temperature of the animal can be determined, and transmitted by the transponder. Typically, the transponder includes a circuit which is connected to the thermistor and measures the resistance of the thermistor by supplying a known current, and measuring the voltage across the thermistor. The voltage is then measured and a temperature value derived from the voltage measurement correlated to the known resistance characteristics of the thermistor.
As will be understood, because an implantable transponder is a passive device, it is highly desirable to have the implantable transponder consume little power. However, traditional thermistor based temperature sensors increase power consumption by requiring a predetermined current be supplied to the thermistor. This additional current increases the power consumption of the transponder significantly. Accordingly, it would be advantageous to have an implantable transponder capable of transmitting temperature information, and which also consumes less power than thermistor transponders which are capable of transmitting temperature information.
Generally, the manufacture and assembly of a temperature sensing transponder requires additional resources compared to the manufacture and assembly of a typical identification transponder. Assembly of a temperature sensing transponder is generally done after the components comprising the identification subassembly of the transponder and the components comprising the temperature sensor or thermistor have been manufactured and/or assembled. The two manufactured subassemblies or components are then combined in a separate manufacturing step. This separate manufacturing step can take a significant amount of time and resources, ultimately increasing the cost of such a transponder. As will be understood, it is advantageous to have such a transponder which is relatively inexpensive, and thus more affordable for a user who wishes to purchase the device. Accordingly, it would be advantageous to have a temperature sensor which is integrated within the normal identification components, thus reducing the costs of such a transponder by not requiring the additional components or the additional step of assembling the transponder with a separate temperature sensor.
While traditional transponders with associated temperature sensing have been somewhat successful in the past, there are several disadvantages associated with them. For example, each thermistor is required to be calibrated, in order to ensure that an accurate temperature is delivered to a user. Such a calibration is performed following the full assembly of the transponder. The assembled transponder is generally placed in a liquid bath having a known temperature. An initial temperature reading is determined using the transponder. This initial temperature reading is compared to the known temperature of the bath, and a compensation factor is determined for the transponder. This compensation factor is typically stored in a memory location within the transponder, and sent to the scanner together with the sensed temperature information requiring the scanner to perform a calculation to determine the temperature of the animal.
In addition, the calibration process is very labor intensive, further adding to the ultimate cost of such a temperature sensing transponder. Each transponder is individually calibrated because each transponder must be assembled with a temperature sensor prior to any calibration. As transponders are typically mass produced in large quantities, individual calibration can add a significant expense to the cost to manufacture such a transponder. Therefore, it would be advantageous to perform a temperature calibration in a more efficient manner, such as prior to the assembly of the transponder.
Furthermore, traditional transponders having associated temperature sensors typically transmit identification information and temperature information in a unique transmission format. For example, different manufacturers employ unique communication schemes which require particular interrogators to be able to read their transponders. Thus, one manufacturer's transmission format may not be able to be read by scanners which were not specifically designed to read such information, i.e., a competitor's scanner. This can be disadvantageous because, in the event that an animal having such a transponder becomes lost or stolen, the transponder can be used as a means of identification for the animal. However, if a scanner is used to attempt to scan a transponder and does not recognize the unique format for its identification information, the scanner will be unable to determine the identification information which is stored in the transponder. Thus, it would also be advantageous to have a temperature sensing transponder which is able to transmit identification information in a format which is able to be read by most common scanners.